Fixes drcachesim delayed tracing which was broken by commit 72275ad4 for #4496 (closed) via PR #4507. The fix is to decorate the target PC to indicate the ISA mode.
Adds a reminder to the dr_flush_region_ex() documentation where it talks about using dr_redirect_execution() to set the ISA mode.
Tested on ARM: $ bin32/drrun -t drcachesim -trace_after_instrs 20000 -- suite/tests/bin/simple_app
Fixes #4527 (closed)